I also reported this issue in the top thread, however I see that there is a thread just for it so I am adding my reply here.

When multiple windows are in a "groupy" group, I am unable to snap (drag to top of screen to maximize, drag to left/right to auto adjust for half screen (left or right respectively) the groupy window.  The individual applications are still able to snap and resize but for some reason groupy does not conform to this behavior.

Per your question.  I am grabbing on to the title bar for the groupy window and not the applications individually.

I'd say it is natural for us to drag from the outer window title bar. in the groupy case, that means the groupy bat itself. It would be more natural to drag the whole group to a screen edge to have it "dock" the same way a regular window does. I noticed that by dragging from the app window bar it does work, and the effect is the whole group getting docked and resised. I guess it would be more natural that the groupy bar would behave the same.